The objective of the proposed research program is to determine the localization and nature of opiate receptors in the central nervous system. Human brain tissue obtained at autopsy will be utilized to study the distribution of stereospecific opiate binding sites and to learn whether these sites have the same or different characteristics in different regions of the human brain. Comparisons of receptor distribution in post-mortem brains of addicts and of non-addicted individuals are planned. These studies will be complemented by research in monkeys utilizing stereotactic techniques. Microinjection of opiates and opiate antagonists as well as specific lesions will provide further information on the sites of action of opiates and on possible relationship between opiates and neurotransmitter substances. Both acute and chronic experiments will be performed.